Thermoplastic polymers, such as polypropylene (PP), polyethylene terephthalate (PET), and styrene-butadiene copolymer (SBC), are used in film and packaging applications. One such application includes multilayer films used in food packaging. Some polymers used in food packaging applications, such as blow molded bottles used for bottling water, are preferentially higher in clarity than other polymers.
PET is currently widely used for high clarity applications because of its relatively low level of melt fracture due to the blow molding process. Blow molded PP and SBC films exhibit surface haze due to melt fracture that occurs during the blow molding or film extrusion process. Conventional process additives (PA's), such as fluoropolymer PA's, siloxane PA's, and the like, used in blow molding PP and SBC film extrusion provide a reduction in melt fracture and, thereby, surface haze. However, these conventional PA's form droplets within the thermoplastic film layer (PP and SBC layer), which result in light scattering that creates internal haze.
PP has a refractive index ranging from 1.45 to 1.5. SBC has a refractive index ranging from 1.5 to 1.59.
Siloxane PA's are known as potential process additives that can be used in thermoplastics for extrusion applications. Siloxane polymers used in these siloxane PA's have unique properties derived mainly from the physical and chemical characteristics of the siloxane bond. These properties include low glass transition temperature, thermal and oxidative stability, resistance to ultraviolet radiation, low surface energy and hydrophobicity, high permeability to many gases, and biocompatibility. The siloxane polymers, however, often lack tensile strength. The resulting siloxane PA's are typically fluidic with very low glass transition (Tg) values at room temperature, and flow at room temperature and above without the need for elevated temperatures. Because of their fluidity at ambient conditions, these siloxane PA's are difficult to process. For example, these siloxane PA's can not be maintained in pellet form at ambient conditions. This makes it difficult to precisely blend the siloxane PA's with thermoplastics for extrusion applications.
There exists a need for a PA that can be used in thermoplastics in extrusion applications in order to obtain improvements in physical properties, such as haze, viscosity, and the like. There also exists a need for using a PA in thermoplastics in extrusion applications while reducing processing pressure at various processing conditions. There also exists a need for a PA that is easy to handle at ambient conditions and can be used in pellet form for extrusion applications.